A. Field of Invention
This invention pertains generally to cathode ray tube (CRT) signal alignment and more particularly to dynamic rotation of the raster upon the face of a CRT.
B. Definitions
Align means to cause a video image to be adjusted so that distortion characteristics are minimized and the video image that is displayed on the cathode ray tube forms an image that is pleasing to the eye.
Alignment camera means the video camera used to generate a signal that is representative of the image displayed on the cathode ray tube in a manner described in U.S. Pat. No. 5,216,504.
Bar code means any sort of optically encoded data.
Cathode ray tube means the tube structure, the phosphor screen, the neck of the tube, the deflection and control windings, including the yoke, rotation and other coils, and the electron guns.
Characterization module means a device that is coupled in some manner to a cathode ray tube and may include a storage device for storing correction factor data or an identification number for the cathode ray tube, and/or a processing device such as a micro-processor or other logic device, and/or driver and correction circuits, and/or control circuitry. The characterization module can also store term multipliers for use in aligning monitors that employ standard transformation equations.
Coordinate locations means the discrete physical locations on the face of the cathode ray tube, or a physical area on the CRT screen.
Correction and driver circuitry means one or more of the following: digital to analog converters, interpolation engine, pulse width modulators and pulse density modulators, as well as summing amplifiers, oscillators, op-amps, inverters comparators or any other components necessary to produce and condition correction signals to synchronously apply to control circuitry to generate an aligned video image.
Correction control signals means correction factor signals that have been combined in a manner to be applied to either horizontal control circuitry, vertical control circuitry, coils, or electron gun circuitry. Correction factor data comprises the encoded digital bytes or any other form of data, such as term multipliers that adjust standardized transformation equations, that are representative of the amount of correction required to align a video signal at a particular physical location on a cathode ray tube to counteract distortion characteristics at that location. Correction factor data may include data from the gain matrix table, data relating to electron gun characteristics and/or data relating to geometry characteristics of the cathode ray tube.
Correction factor parameters include various geometry characteristics of the cathode ray tube including horizontal size, raster rotation, vertical size, horizontal center, vertical center, pincushioning, vertical linearity, keystoning, convergence, etc., and various electron gun characteristics of the cathode ray tube including contrast, brightness, luminosity, focus, color balance, color temperature, electron gun cutoff, etc.
Correction factor signals means digital correction signals that have been integrated or filtered.
Correction signals means digital correction signals and correction factor signals.
Decoder means a device for generating an electronic signal in response to one or more data bytes that may include PWMs, PDMs, DACs, interpolation engines, on screen display chips, etc.
Device means any apparatus which incorporates a cathode ray tube as part of its implementation.
Digital correction signals means signals that are generated by decoders, such as pulse width modulators, pulse density modulators, digital to analog converters, etc. in response to correction factor data.
Digital monitor board means a circuit board that includes one or more of the following: vertical control circuitry, horizontal control circuitry, electron gun control circuitry, correction and driver circuitry, a logic device, digital to analog converters, and a memory. A Digital monitor board may comprise an actual chassis monitor board used with a particular monitor, an ideal chassis board, a chassis board that can be adjusted to match the characteristics or specifications of a particular monitor board, etc.
Digitized signal is any electrical signal that has a digital nature.
Direction means up, down, left, right, clockwise anti-clockwise, brighter, dimmer, higher, lower, etc.
Discrete locations may mean individual pixels on a cathode ray tube screen or may comprise a plurality of pixels on a cathode ray tube screen.
Distortion characteristics means the amount of any particular type of distortion as indicated by the distortion data measured at a number of different points on the cathode ray tube.
Distortion data is a measure of the amount of distortion that exists on a cathode ray tube with regard to the geometry characteristics of he tube, and/or electron gun characteristics of the tube. For example, distortion data can be measured as a result of misalignment of a video image or improper amplitude or gain of a video signal. Distortion data can be a quantative measure of the deviation of correction factor parameters from a desired quantative value. Distortion data can be measured at coordinate locations on the cathode ray tube.
Driver signals are the electrical signals that are used to drive the deflection and control windings, and electron guns of the cathode ray tube.
Frame grabber means an electronic device for capturing a video frame.
Gain matrix table means a table of values that are used to indicate how a change in correction factor data for one correction factor parameter influences the change in the correction factor data for other correction factor parameters, as disclosed in U.S. patent application Ser. No. 08/611,098, filed Mar. 5, 1996, entitled "Method and Apparatus for Making Corrections in a Video Monitor".
Internal to raster means any part or section of a CRT raster as defined by its location on the raster.
Interpolation engine means a device for generating continuously variable signals, such as disclosed in U.S. patent application Ser. No. 08/613,902 filed Mar. 11, 1996 by Ron C. Simpson entitled "Interpolation Engine for Generating Gradients."
Logic Device means any desired device for reading the correction factor data from a memory and transmitting it to correction and driver circuitry, including a micro-processor, a state machine, or other logic devices.
Magnetic strip means any sort of magnetic storage medium that can be attached to a cathode ray tube.
Maximum correctable distortion data means the limits of the distortion data for which an aligned video signal can be generated for any particular cathode ray tube using predetermined correction and driver circuitry, and control circuitry.
Memory comprises any desired storage medium including, but not limited to, EEPROMs, RAM, EPROMs, PROMs, ROMs, magnetic storage, magnetic floppies, bar codes, serial EEPROMs, flash memory, etc.
Non-volatile electronic storage device means an electrical memory device that is capable of storing data that does not require a constant supply of power.
Pattern generator means any type of video generator that is capable of generating a video signal that allows measurement of distortion data.
Processor means a logic device including, but not limited to state machines, micro-processors, etc.
Pulse density modulation (PDM) means a device for generating pulse density modulation signals in response to one or more data bytes, such as disclosed in U.S. patent application Ser. No. 08/611,098, filed Mar. 5, 1996 by James R. Webb et al. entitled "Method and Apparatus for Making Corrections in a Video Monitor".
Pulse width modulator (PWM) means a device that generates pulse width modulated signals in response to one or more data bytes, such as disclosed in U.S. patent application Ser. No. 08/611,098, filed Mar. 5, 1996 that is cited above and U.S. Pat. No. 5,216,504.
Raster means all or part of the horizontal traces produced on the face of a CRT.
Rotation coil means a coil or winding used to rotate the raster in a CRT.
Rotational correction factor data means electronic data generated by a vision system in response to rotational distortion characteristic measurements obtained the vision system. The rotational correction factor data may be stored as term multipliers which are used to modify standardized transformation equations and parametric data as disclosed in U.S. Pat. No. 5,216,504, issued Jun. 1, 1993 entitled "Automatic Precision Video Monitor Alignment System". Alternatively rotational correction factor data may be obtained by screen mapping with a vision system and stored for later use as disclosed in U.S. patent application Ser. No. 08/638,222 filed Apr. 26, 1996, entitled "Screen Mapping of a Cathode Ray Tube".
Rotational distortion characteristics means the amount of rotational distortion as indicated by the rotational distortion data measured at a number of different points on a cathode ray tube.
Rotational distortion data is a measure of the amount of rotational distortion that exists on a specific cathode ray tube with regard to the geometry characteristics of the tube. For example, rotational distortion data can be a result of misalignment of a video image on the face of the CRT. Rotational distortion data can be a quantitative measure of the deviation of rotational correction factor data from a desired quantitative value. Rotational distortion data can be measured at coordinate locations on the cathode ray tube.
Rotation driver signals means time dependent analog signals generated, by various methods, and applied synchronously to the CRT rotation coil to dynamically align traces of the CRT raster display.
Storage disk comprises any type of storage device for storing data including magnetic storage devices such as floppy disks, optical storage devices, magnetic tape storage devices, magneto-optical storage devices, compact disks, etc.
Term multipliers means factors generated by measuring distortion characteristics of a CRT for use with transformation equations to produce a correction signal.
Time Variable Rotation Driver Signal means a changing level correction signal, with a maximum period of one vertical CRT scan, applied to a coil of a CRT to rotate the horizontal traces of the electron beam on the CRT face.
Transformation equation means a standard form equation for producing a correction voltage waveform to correct common distortion characteristics of a cathode ray tube.
Variable Resistor means an apparatus capable of producing a changeable value of electrical resistance.
Video image means the displayed image that appears on the cathode ray tube screen that is produced in response to a video signal.
Video pattern is the video image of a pattern that appears on the cathode ray tube raster as a result of the video signal generated by the pattern generator.
Video signal means the electronic signal that is input to the electron guns of the cathode ray tube.
Vision System means any automated method for measuring CRT distortion characteristics generating distortion data and producing correction factor data, including rotational correction factor data that is used in the alignment of a raster on a cathode ray tube.
Waveform Generator means an apparatus for producing an electronic signal with a desired shape amplitude and period.
C. Description of the Background
Recent developments in measurement of distortion and automated alignment of CRT displays in devices such as computer monitors and digital television have made it possible and desirable to dynamically correct video displays for various types of distortion. Raster rotational distortion has been a type of distortion that it has not been possible to correct dynamically because of the nature of the distortion and its complex relationship with other CRT alignment parameters. Although rotation coils are provided on many CRT's, these coils have not been able to correct various types of rotational distortion occurring internal to the CRT raster. Correcting internal raster distortion is important in providing overall distortion correction since other correction parameters necessary to minimize display distortion are extremely sensitive to raster rotational distortion.
Heretofore, CRT rasters were rotated statically in an analog circuit by adjusting a variable resistor to supply a direct current (DC) correction level to the CRT rotation coil. This method is inherently limited because the same correction is applied over the whole raster. In other words, the entire raster can be rotated in an attempt to correct rotational distortion. However, rotational distortion often varies significantly over the raster. It is not uncommon for the top of the raster to have a different horizontal alignment than the center or bottom. Since prior art devices have been unable to correct for distortion internal to the raster, it would therefore be desirable to provide a dynamic system to accurately maintain rotational alignment of a CRT raster over the entire raster surface.